The following invention relates to a ROM emulator module to be used in conjunction with a diagnostic tester for testing or troubleshooting microprocessor-based electronic systems.
Microprocessor-based electronic systems such as microcomputers require test instrumentation capable of diagnosing and correcting system faults and faulty electronic components. Such diagnostic testers in the past have relied upon the technique of emulating the system's microprocessor or central processing unit in order to control the remainder of the system so that a series of diagnostic tests may be conducted which isolate the system's microprocessor from the remainder of the components. Microprocessor emulation performs two basic functions. In isolating the microprocessor from the remainder of its system components, it ma quickly be determined whether the microprocessor itself is faulty or whether the problem lies in some other component. Second, using an emulator to control the remainder of the system, rather than the system microprocessor, allows the diagnostic tester much more flexibility in exercising the remaining components of the system which might not otherwise be possible. This is due to the fact that the microprocessor in the system depends in large amount upon other system components in order to execute programs, and it is very likely that one or more of these other components could be the source of the problem. The diagnostic test routines can effectively remove these components from the system selectively or exercise these components from the microprocessor emulator in such a way that their functions are isolated from one another and diagnosis of the system may proceed in an orderly fashion.
The problem with such testers is, however, that they are expensive. A diagnostic tester using the microprocessor emulation technique is unique to the particular microprocessor used in the device under test (DUT). Since there are a large variety of different microprocessors currently in use in various types of systems, it can be very expensive to acquire a plurality of evaluators, one for each type of microprocessor. Due to the wide variations of ways in which microprocessors are structured, there is, as yet, no general-purpose microprocessor emulator available.
What is needed therefore, is a universal diagnostic test device which is capable of being used with any type of microprocessor without requiring separate circuitry for each type of microprocessor that might be encountered.